Re: [PATCH v2 4/4] mmc: sdhci_am654: Fallback to DT-provided itap delay on DDR50 tuning failure

Hi Judith,

Thanks for the review!

On 8/3/26 9:59 PM, Mendez, Judith wrote:
> Hi Diogo,
> 
> Thanks for your patch, couple of doubts below.
> 
> On 8/3/2026 8:47 AM, Diogo Ivo (Schneider Electric) wrote:
>> DDR50 mode is not required to support the tuning command CMD19, meaning
>> that calibration may fail on cards that do not implement it, in which
>> case a known-good itap delay value should be programmed into the host
>> controller.
>>
>> Do this by reading the (already defined) itap delay DT property for DDR50
>> and, if tuning fails for this mode, fall back to the DT-provided itap 
>> delay
>> value. If the DT does not provide a value for DDR50 fallback then this
>> simply disables using itapdly.
>>
>> Fixes: 901d16e46296 ("mmc: sdhci_am654: Add retry tuning")
> 
> Should this commit be the one to blame or should it be the commit that
> introduces DDR50 support?

I'm not sure I follow you here, as I wasn't able to pinpoint a commit
that specifically introduced support for DDR50. Could you please clarify?

Taking a look at the git log of the driver I see a0a62497f6aa, where
reading itapdly from DT was added but without reading the DDR50 value
and 13ebeae68ac9, the commit where tuning was originally added, but the
"responsibility" seems split between the two.

>> Cc: <[email protected]>
>> Signed-off-by: Diogo Ivo (Schneider Electric) <[email protected]>
>> ---
>> Changes in v2:
>>   - As suggested by Sashiko save values read from DT for DDR50 in 
>> separate
>>     variables in order to keep them across multiple tuning cycles without
>>     overwriting them.
>> ---
>>   drivers/mmc/host/sdhci_am654.c | 25 ++++++++++++++++++++-----
>>   1 file changed, 20 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci_am654.c b/drivers/mmc/host/ 
>> sdhci_am654.c
>> index 8ce10422bba0..27ef79420eba 100644
>> --- a/drivers/mmc/host/sdhci_am654.c
>> +++ b/drivers/mmc/host/sdhci_am654.c
>> @@ -126,7 +126,7 @@ static const struct timing_data td[] = {
>>                      NULL,
>>                      MMC_CAP_UHS_SDR104},
>>       [MMC_TIMING_UHS_DDR50]    = {"ti,otap-del-sel-ddr50",
>> -                   NULL,
>> +                   "ti,itap-del-sel-ddr50",
>>                      MMC_CAP_UHS_DDR50},
>>       [MMC_TIMING_MMC_DDR52]    = {"ti,otap-del-sel-ddr52",
>>                      "ti,itap-del-sel-ddr52",
>> @@ -144,6 +144,8 @@ struct sdhci_am654_data {
>>       u32 otap_del_sel[ARRAY_SIZE(td)];
>>       u32 itap_del_sel[ARRAY_SIZE(td)];
>>       u32 itap_del_ena[ARRAY_SIZE(td)];
>> +    u32 itap_del_sel_dt_ddr50;
>> +    u32 itap_del_ena_dt_ddr50;
>>       int clkbuf_sel;
>>       int trm_icp;
>>       int drv_strength;
>> @@ -579,10 +581,18 @@ static int 
>> sdhci_am654_platform_execute_tuning(struct sdhci_host *host,
>>       } while (++tuning_loop < RETRY_TUNING_MAX);
>>       if (itapdly < 0) {
>> -        dev_err(dev, "Failed to find itapdly, fail tuning\n");
>> -        sdhci_am654_write_itapdly(sdhci_am654, 0, 0);
>> -        sdhci_am654->itap_del_ena[timing] = 0;
>> -        sdhci_am654->itap_del_sel[timing] = 0;
>> +        if (timing == MMC_TIMING_UHS_DDR50) {
> 
> Should dev_dbg be added here to let the user know that tuning failed but
> DT defaults were set?

That sounds useful, I'll add a print here.

> ~ Judith
> 

Best regards,
Diogo